TRANSCRIPTIONAL REPRESSION DIRECTED BY THE YEAST ALPHA-2 PROTEIN IN-VITRO

THE alpha 2 protein, a homeodomain protein involved in specifying cell type in the budding yeast Saccharomyces cerevisiae, is a transcriptio nal repressor(1,2). alpha 2 binds cooperatively with Mcm1, a serum res ponse factor-related protein, to the a-specific gene operator(3-6). Th e alpha 2-Mcm1 complex in turn recruits Ssn6 and Tup1 to the operator, and we believe that these latter two proteins are responsible for the transcriptional repression(7-9). Placement of the a-specific gene ope rator in any of a variety of positions upstream of a test promoter lea ds to repression of that promoter in vivo(9-11). In this respect, the a-specific gene operator resembles a negatively acting enhancer. Here we describe the in vitro reconstitution of this example of negative co ntrol from a distance. We observe repression in vitro in the absence o f exogenously added activator protein and on templates that lack bindi ng sites for known activator proteins, and we infer that alpha 2-direc ted repression acts on the general transcription machinery.